Nutritional exposures in early life can have a long-lasting effect on cardiovascular disease (CVD) risk in adulthood. However, few specific dietary factors have been identified, and the time windows when they are more likely to influence later CVD risk are uncertain. Fatty acids, especially long-chain polyunsaturated fatty acids, have well-recognized effects on CVD risk factors in adults, but their roles in early life remain unknown. Serum fatty acids concentrations are adequate biomarkers of dietary intake. The goal of this application is to study the associations of serum fatty acid concentrations during infancy and childhood with 1) BMI trajectories from infancy through adolescence and 2) cardiometabolic risk factors at age 16 y in a well-established cohort of Chilean children. We will measure fatty acids concentrations in stored serum samples of 750 cohort participants who have a sample available at infancy (6 to 18 mo) plus samples at 5 and/or 10 y of age. Endpoints of interest include change in body mass index from infancy through adolescence (age 16 y) as well as CVD risk factors measured at age 16 y including % body fat (from DXA), blood pressure, insulin resistance (HOMA), lipid profile, inflammatory markers, and adipokines. We hypothesize that long chain n-3 polyunsaturated fatty acids (PUFA) in infancy or childhood are inversely related to the development of adiposity and related metabolic disturbances. Conversely, n-6 and trans-fatty acids are positively associated with these outcomes. Because fatty acid status is potentially modifiable through dietary interventions, this study could provide a basis for early interventions in children aimed at decreasing the burden of CVD. The Chilean cohort is ideal for the study of the development of adiposity-related metabolic disturbance because the years of enrollment in infancy corresponded to a period of extremely rapid transition to high rates of child obesity. This is a highly cost-effective study since a wealth of data and samples has already been collected.